Pseudorabies, also called Aujeszky's disease, is an acute infectious disease caused by Suid herpesvirus 1 (SuHV1) belonging to the Alphaherpesvirinae subfamily for many kinds of livestock such as swine, cattle and sheep, as well as poultry and wild animals, with the main symptoms of fever, intense itching (except swine) and encephalomyelitis. Pseudorabies in swine is found nationwide in China causing severe damages, and is one of the major diseases limiting the large-scale production of pig farms. Infection can result in abortion, stillborn or mummified fetuses in pregnant sows, and neurological signs, paralysis and a high death rate in piglets. Pseudorabies virus (PRV) with strong pantropic properties, neurotropic properties and latent infectivity, may establish long-term latent infection in the peripheral nervous system, and then the latently infected host starts to get sick when the latent virus is activated into the infectious virus.
It has been indicated by many researches that a corresponding protection can be provided for the vaccinated animals by a subunit vaccine, which is a vaccine prepared by cloning the protective antigen genes of pathogen into prokaryote and eukaryote expression systems with methods of genetic engineering so as to highly express those genes. It has been found so far that either of glycoprotein B, C and D (gB, gC and gD) in the PRV glycoproteins can make the body generate neutralizing antibodies, which have the ability to neutralize PRV, no matter in vivo or in vitro, or no matter with the presence or absence of complements. The article, Progress in Subunit Vaccine against Pseudorabies Virus Development (Chenghuai Yang, Gaoming Lou, Nanhui Chen, Jiangxi Journal of Animal Husbandry & Veterinary Medicine 2004 Issue 3) has disclosed that either of gB, gC and gD among 11 PRV glycoproteins which have been found so far, can induce the body to generate neutralizing antibodies. In the absence of complements, monoclonal antibodies directed against gB, gC and gD can neutralize PRV. The swine and mice injected with monoclonal antibodies directed against gB, gC and gD can resist attacks by virulent PRV strains. Therefore gB, gC and gD are the most preferred proteins for developing PRV subunit vaccine. The glycoprotein, gD, is an important neutralizing antigen as well as the main target for protective antibodies, and it can induce better protective response. As disclosed by U.S. Pat. No. 6,858,385 and U.S. Pat. No. 6,521,231, vaccine for preventing pseudorabies can be prepared by use of gD of porcine pseudorabies virus.
The porcine PRV has only one serotype, thus usually the cross-protection immunity between strains of porcine PRV is considered to be very strong. However, piglets may still suffer from typical porcine pseudorabies after their injection with commercial vaccines, with symptoms such as long-term high fever, depression, loss of appetite, respiratory and/or neurological signs. The significant manifestations include that infection among swine at any ages, horizontal transmission among swine herds, short incubation period (1˜2 days), morbidity rates between 10%˜100%, mortality rate in pigs between 10%˜100% (mortality rate in piglets can reach up to 100%), high fever in pigs after being infected (40° C.˜42° C., lasting for more than 3 days), dyspnea, diarrhea, wheezing, coughing, sneezing, hind limb paralysis, dog sitting, suddenly falling down, convulsions, lying on their sides, opisthotonus, making strokes with their arms, and finally dying of exhaustion, and the infection also can cause reproductive disorder symptoms such as declined semen quality of boar, as well as abortion of pregnant sow (the abortion rate can reach up to 35%), premature birth, stillbirth, weakened piglets (weakened piglets die by 14 days of age), etc. By means of prior art, vaccinated pigs cannot completely resist attacks by the wild virus, and still have symptoms like high fever, depression, partially or completely loss of appetite, with a infection rate of more than 30% and a mortality rate between 10% and 20%. There are no vaccines in the prior art capable of solving the pseudorabies caused by variant strains of porcine pseudorabies virus.